Rats in cavity wall

Postby bornlivelife » Fri Nov 09, 2007 11:50 am

This is my first post and have a really difficult problem Im hoping someone might have some ideas how to help.

Have a full width single storey flat room extension on back of a semi, and there are rats in the roof. Poison put down kills them off for 2 weeks, then they return ao need permanent fix.

Have sealed all cavity walls in extension at head height and this barred them from the roof but they were still in walls. Found a loose brick below damp course in main house where it joins extension, pulled it out and found a lot of gaps between bricks where a gas pipe had been put in, so put loads of concrete in below damp course and sealed it. This barred the rats from walls.

2 weeks later they are back in roof of extension, but previous work is still perfect, ie they must have another route into the extension roof, between ceiling and flat roof. There are no external gaps in roof and the walls are all perfect above ground level. There are no holes in garden

Putting posion in drains kills the rats for 2 weeks so there is some connection between drains and flat roof

Conclusion: I think the rats are in main house (built 1959) back wall cavity which the extension (built 1991) is joined to. I think somehow the drains are connected to this cavity possibly from previous kitchen sink drain. Think they are getting into flat roof extension through hole for electric supply into roof


1. Can i seal the main house cavity wall with anything that rats will not penetrate?
2. Do i still need the air in this cavity wall, as it is not internal since extension was built?
3. Would a smoke pellet in cavity wall show me where the holes are?
4. What can I do !!
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Postby blackcat » Fri Nov 09, 2007 9:11 pm

ok the only advice i can give you is to get a pest control guy to give you a look.... rat will gnaw anythink and everthink is your house detached or a semi its a nasty one ps beware of viles disease as this is carryed in they urine a real nasty peice of work sorry but thats it
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Postby bornlivelife » Fri Nov 09, 2007 9:52 pm

thanks for replying!

pest control people will only know how to kill rats though, which i know how to do anyway

what i need is a way of sealing the property, ie a builder who knows how to do it
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Postby blackcat » Sat Nov 10, 2007 9:03 pm

ok i under stand that but rats... mice they have a knack of finding a weak spot have you wooden floors as you know there will be a gap under the boards and being a semi you have next door to deal with sorry but i have seem then every where and anywhere
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Postby thedoctor » Sun Nov 11, 2007 7:33 pm

bornlivelife. In another post in this forum you accuse the forumof having no experts to solve your rat problem and state this should be an easy problem for a builder. It is not and as correctly stated above there are at least 100 ways a determined rat can get into a building if it wants to including, in our own experience, chewing through a live electric cable to get access to the void it filled. The only answer but one you choose to ignore, is a pest control officer who will eliminate the present rats and any future infestations. There is absolutely no such thing as a rat proof house and they must have chosen your house for a reason so give the pest control officer a chance to find out why.
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Postby bornlivelife » Sun Nov 11, 2007 9:40 pm

yes it sounds good but i have tried several and all they do is put posion down, kill them, and they are back in 2 weeks

Thats why i was seeking advice from professional builders like yourselves, as a pest control officer couldnt possibly know what you know.

Honestly we know rats are in the drains, and think an underground pipe was not blocked off when the drains were moved on building extension - somehow the whole lots has opened up and possibly come loose underground allowing access inside cavity walls.

O am now thinking about pumping or hand pushing concrete inside to try and block the probable void
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Postby oldhenry » Fri Nov 30, 2007 8:00 pm

You need to keep killing them until the whole family is dead. they are not solitary animals. Everyone
is around 9 metres from a rat - on average, so need to be wary and leave no food out for them at all. They only come to houses for food. All cavities should be closed at roof level when the property was built, they can climb pipes and get into eaves, as do squirrels- which are rats to me-. otherwise they squeze round pipes.no ther way , unless you let them up th estairs. Do you have a cat?, brilliant at killing things, I have one.
Set traps for rats, wire ones, then you can kill them later, which is more satisfying- I think.
There must be a nest near you. It is not a building problem, otherwise everyone would have this. Some times the poison has to be left for weeks to kill a large family. Keep on to it.
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Postby goffchris » Fri Jun 12, 2009 7:36 am

I have the same problem, and I had an idea that will kill another bird (or rat) with the same stone, save money, and avoid releasing poisons into the environment:

Cavity Wall Insulation!

Cavity wall insulation is usually a foam that is sprayed into the cavity through holes drilled in several places along the wall. This effectively removes the space the rats and mice use to crawl around the walls of the building. At the same time it has this effect, it also saves you money on heating!

Now, my problem is that I live in an ex-local authority flat which faces onto Southwark Park Road. I was told that they would need a cherry-picker to do the back wall, and that I would have to hire one for them! I have been after Southwark Council to do the whole estate, but no luck so far!
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Postby Zecis » Wed Nov 25, 2009 8:25 am

I saw this post.... I have had the same problem.... be careful poisoning the beasts. They then die in inaccessible places and decompose slowly. We have had hordes of bluebottles for most of the summer - and rats (that I tried to poison) last winter. Eventually I gave up and called the rat man... (Free from the local council here in Wiltshire). I told him the problem, he immediately warned of the danger that they die where you can not reach them - apparently the smell can be .... well you can imagine.
So be careful with poison.

Good luck
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Postby acsimpson » Thu Nov 26, 2009 10:28 am

[quote="goffchris"]Cavity wall insulation is usually a foam that is sprayed into the cavity through holes drilled in several places along the wall. This effectively removes the space the rats and mice use to crawl around the walls of the building. At the same time it has this effect, it also saves you money on heating![/quote]

You need to be carefull with the sprayed foam cavity wall insulation. It may be the best for stopping rats but a simple google search will provide plenty cases where it has caused problems from cracking weak walls to creating damp problems.

The best option currently available is carbon eps beads. They are the most efficient for keeping heat in and moisture out.
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Postby sarah01 » Tue Dec 08, 2009 2:26 pm

We have a problem where rats are getting into our kitchen ceiling. This is a new rear kitchen extension, approx 2 yrs old. The rats have chewed through the rockwall insulation which fills the cavity between the london stock brick on the outer wall and the breeze block on the inner wall. We plan to take the plasterboard ceiling down and fill any holes with concrete mixed with broken glass...... cannot think of anything else to do. There is solid poison up there but they eat it then die leaving a stench. The light fittings are a reasonable size so we can pull those down to stick a gloved hand in and possibly remove any dead ones.

Does anyone else have any ideas?? The pipe work running under the house has been inspected and is all ok. The wall where they have got under is right next to the rodding eye that the builders installed so thus the sewer runs around there. If there was a broken pipe we would have other signs, would we not??? water, soggy ground / patio?? Bad smells, other than decaying rat.

This is a nightmare issue. Can anyone shed any light on this issue. I have had rat pest controllers onto the issue ie the guys who did the bbc programme recently. They are great but they say we can keep on killing them until we find out where they are coming from. How does one do this when it is under the house??

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Postby vijendrasnv » Tue Dec 29, 2009 7:19 pm

Many of us had the same problems with the rats on the ceiling or in the dump wooden blocks.The solution is proper insulation in the wooden items so these might get not tampered.So the best solution is Cavity Wall Insulation also mentioned above.
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Postby xboxdevil » Mon Jan 18, 2010 11:25 am

Yes ring up the council, they did a free smoke bomb test for us and it clearly identified where the break in the sewer was.

There will be a break in either your sewer pipe or a neighbour in an adjourning house; we had the same problem a couple of years back.
We got Dynorod to come and do a camera inspection, it came back ok, but the rats kept coming back, in the end I dug down to the main soil pipe as it exited the house, no break but the seal had failed and when the toilet was flushed you could see water spilling out, although this was about foot up from the bottom of the pipe this was the entry point, they get in then they climb the first thing that they can as they forage for food.

Good luck, I am only too aware of how disheartening the whole cycle is.
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Postby sarah w » Thu Mar 18, 2010 9:25 pm

A few years ago we had rats getting into our kitchen extension(built in 1970's) this drove us nearly mad. Eventually a builder who was a friend of ours(he knew about the problem) replaces the extension roof, floor and fitted a new kitchen.We found 7 large dead rats in our ceiling!

All the holes were sealed and a proper drain cover was fitted onto the drain under the extension. He did a great job and we havent heard any noises in the extension since.

We recognised the smell or a dead rat a few days ago. Speaking to our neighbours(we live in a terraced row)they have heard scratching and put poison down...

Where the back door had been moved for the extension it had been replaced with plasterboard. We have taken this out which showed the hollow cavities. To our shock the cavity has no floor and is entirely open to the underground running the entire lengh of the house! Is this normal? We feel now there is nothing we can do to stop the rats climbing the walls.

The loft cavities are sealed from the top, we have got a cat now who is frightened of his own shadow! What an exhausting position to be in. I feel we have done so much and now found NO floor in the cavities. Perhaps it is normal? Any ideas?
sarah w
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Postby avr » Sun May 08, 2011 4:52 pm

We have the exact same problem and would love to know whether you resolved the problem via drains - is it over for you yet? The extension was built before our purchase of the property 6 years ago. However, it has only been a problem for the past 9 months within the house and has continued to worsen with rats now gaining access to other ceiling areas in the house. Pest control conducted a drain survey but weren't convinced that their equipment would pick up the fault - they are convinced it is from the drains. They have laid poison numerous times. We are getting pretty desperate.
Look forward to any latest news from you.
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